The analysis of clinical or environmental fluid samples generally involves a series of chemical, optical, electrical, mechanical, or thermal processing steps on the samples. In recent years, there has been growing interest in developing disposable cartridges for conducting analyses of biological samples for various diagnostic and monitoring purposes. For example, U.S. Pat. No. 5,587,128 to Wilding discloses devices for amplifying a preselected polynucleotide in a sample by conducting a polynucleotide amplification reaction. U.S. Pat. No. 5,922,591 to Anderson et al. describes a miniaturized, integrated nucleic acid diagnostic device and system. The device is generally capable of performing one or more sample acquisition and preparation operations, in combination with one or more sample analysis operations.
Prior fluidic cartridges for processing fluid samples have focused on picoliter, nanoliter, and microliter sample volumes. These small sample volumes are not practical for many realistic diagnostic applications. Of special interest is the detection of target analytes (e.g., nucleic acid) that exist in low concentrations in many samples. For example, in detecting infectious diseases, gram negative bacteria can be present at less than 10 copies per milliliter of blood, cryptosporidium generally appears as only a few copies per gallon of drinking water, concentrated biothreat agents (e.g., anthrax) at less than 100 copies per milliliter of water, and food poisoning agents, such as E. coli and salmonella, may be manifested in less than 10 copies per gram of food.